Using state processor for a custom windowed aggregate function

[Alexis Sarda-Espinosa]

Hello,

I am trying to create state for an aggregate function that is used with a
GlobalWindow. This basically looks like:

savepointWriter.withOperator(
    OperatorIdentifier.forUid(UID),
    OperatorTransformation.bootstrapWith(stateToMigrate)
        .keyBy(...)
        .window(GlobalWindows.create())
        .aggregate(new AggregateFunctionForMigration())
)

The job runs correctly and writes a savepoint, but if I then read the
savepoint I just created and load the state for that UID, the "elements"
iterable in the WindowReaderFunction's readWindow() method has a non-zero
size, but every element is null.

I've tried specifying a custom trigger between window() and aggregate(),
always returning FIRE or FIRE_AND_PURGE, but it didn't make any difference.

Am I missing something?

Regards,
Alexis.